Multi-phase metering of fluid flows

Abstract

A multi-phase flow meter includes a flow conduit leading from an inlet to an outlet and including a variable inlet restriction, a variable outlet restriction, a pressure sensor and a volumetric flow meter, located between the variable inlet restriction and the variable outlet restriction. The flow meter further includes a controller adapted to receive data from the pressure sensor and the volumetric flow meter, and to adjust the variable inlet restriction and the variable outlet restriction in accordance with at least one program. The program causes the controller to adjust one of the variable inlet restriction and the variable outlet restriction.

What is claimed is: 
     
       1. A multi-phase flow meter for measuring individual flow rates of oil, water and gas fractions within a fluid flow from an oil well, the meter comprising:
 a flow conduit having a single inlet end and a single outlet end and configured to carry a flow of a multi-phase fluid between the said inlet and outlet ends, 
 a single variable inlet restriction at the inlet end of the flow conduit configured to control the flow of the multi-phase fluid through the inlet end into the flow conduit, and 
 a single variable outlet restriction at the outlet end of the flow conduit configured to control the flow of the multi-phase fluid from the outlet end of the flow conduit, 
 a pressure sensor and a flow meter, located in the flow conduit between the variable inlet restriction and the variable outlet restriction, and 
 a controller adapted to receive data from the pressure sensor and the flow meter, and to adjust the variable inlet restriction and the variable outlet restriction in accordance with at least one program; 
 wherein in accordance with the at least one program the controller is arranged to adjust one of the variable inlet restriction and the variable outlet restriction such that the fluid pressure between them adopts a first pressure, then to further adjust the restriction such that the fluid pressure between the restrictions adopts a second and different pressure, and to record the first pressure, the second pressure, and the fluid flow rates at the first pressure and at the second pressure; 
 whilst adjusting the other of the variable inlet restriction and the variable outlet restriction so that the total flow restriction imposed by the inlet and outlet restrictions is maintained at a substantially constant level, so that the multi-phase flow rate is maintained constant from the well and through the meter. 
 
     
     
       2. The multi-phase flow meter according to  claim 1 , wherein the variable inlet restriction is continuously variable between a minimum restriction and a maximum restriction. 
     
     
       3. The multi-phase flow meter according to  claim 2 , wherein the variable inlet restriction is a monotonic valve that is variable between the minimum restriction and the maximum restriction such that it is capable either of opening but not of closing, or of closing but not opening. 
     
     
       4. The multi-phase flow meter according to  claim 2 , wherein the inlet restriction prevents all flow when at the maximum restriction. 
     
     
       5. The multi-phase flow meter according to  claim 1 , wherein the variable inlet restriction is variable between a plurality of predetermined discrete and repeatable values. 
     
     
       6. The multi-phase flow meter according to  claim 1 , wherein the variable outlet restriction is continuously variable between a minimum restriction and a maximum restriction. 
     
     
       7. The multi-phase flow meter according to  claim 6 , wherein the variable outlet restriction is a monotonic valve that is variable between the minimum restriction and the maximum restriction such that it is capable either of opening but not of closing, or of closing but not opening. 
     
     
       8. The multi-phase flow meter according to  claim 6 , wherein the outlet restriction prevents all flow when at the maximum restriction. 
     
     
       9. The multi-phase flow meter according to  claim 1 , wherein the variable outlet restriction is variable between a plurality of predetermined discrete and repeatable values. 
     
     
       10. The multi-phase flow meter according to  claim 1 , wherein the flow meter is a volumetric flow meter. 
     
     
       11. The multi-phase flow meter according to  claim 10 , wherein the flow meter is an ultrasonic flow meter. 
     
     
       12. The multi-phase flow meter according to  claim 10 , wherein the flow meter is a turbine flow meter. 
     
     
       13. The multi-phase flow meter according to  claim 1 , wherein the controller has a further program that causes the controller to fully close the inlet restriction or the outlet restriction and to open fully the outlet restriction or the inlet restriction, respectively, to maintain this state for a period of time, and to calibrate at least one of the pressure sensor and the flow meter at that time. 
     
     
       14. The multi-phase flow meter according to  claim 1 , further comprising:
 a computing means to calculate the relative fractions of gas and liquid flowing through the flow conduit based on the measured pressures and flow rates. 
 
     
     
       15. The multi-phase flow meter according to  claim 14 , further comprising:
 a mass flow meter located between the inlet and the outlet flow restrictions. 
 
     
     
       16. The multi-phase flow meter according to  claim 15 , wherein the computing means is further arranged to calculate the relative fractions of different liquids based on the measured and mass flow rates.